Structural and dynamical behavior of Al trimer on Al(111)surface

Trimer is the smallest cluster that can have a one-dimensional or two-dimen sional structure on surfaces, and it can diffuse and transform between thes e structures. Using first-principles density-functional theory (DFT) calcul ations, the structural and dynamical behaviors of Al trimer on Al(111) surf ace have been studied in detail. Al trimer on Al(111) surface has three dif ferent kinds of structure conformations (groups with similar configurations ): close-packed (compact) triangular trimers, non-compact triangular trimer s, and linear trimers. The close-packed triangular trimers are more stable than the non-compact triangular trimers and the linear trimers, while most of the non-compact triangular trimers are as stable as the linear trimers. For the dynamics of Al trimer on Al(111) surface, there are three different kinds of diffusion mechanisms: (1) concerted translations and rotation of compact triangular trimers (the highest energy barrier by DFT calculation, E-d=0.24 eV); (2) back-and-forth transformation between compact triangular trimers and linear trimers (E-d=0.21 eV); and (3) translation of linear tri mers (E-d=0.28 eV). Among these different mechanisms with similar height of diffusion barriers, the concerted translations of the compact triangular t rimers have the longest displacement of the center of mass in the least ste ps. Therefore, we expect the long-range diffusion of Al trimer on Al(111) s urface is dominated by the concerted motion process of the compact triangul ar trimers. The concerted translations and concerted rotations of Al trimer on Al(111) surface have also been observed in the molecular dynamics simul ations using the embedded atom method. (C) 2000 Elsevier Science B.V. All r ights reserved.